I. Field of Invention
The present invention relates to a device that warns a pregnant woman when sound pressures are present that may be exceeding a predetermined level to protect the hearing of a pregnant woman's developing fetus.
II. Brief Description of the Prior Art
Seven million workers in the United States are currently exposed to occupational noise. A growing number of these workers are pregnant women. While rather rigid regulations are in force concerning hearing conservation in all workers, including pregnant women, no guidelines are yet available on level and duration of noise exposure for fetuses in utero. Furthermore, high levels of sound pressures are present during recreational activities such as boating and motorcycling. It is known that sounds readily penetrate the uterus, and that sounds of low frequencies can actually be louder inside than outside. Preliminary data suggest that intense sound pressures result in disruption of fetal sleep state and altered fetal hearing sensitivity.
Recent studies by Lalande ["Is Occupational Noise Exposure During Pregnancy a Risk Factor of Damage to the Auditory System of the Fetus?" Nicole M. Lalande, Ph.D., Raymond Hetu, Ph.D., and Jean Lambert, Ph.D. American Journal of Industrial Medicine, 1986; 10:427-435] showed hearing loss in children of mothers who were exposed to noise in the workplace. This hearing loss was greatest when low frequencies were present in the exposure.
Low frequencies can be enhanced within the abdominal cavity of humans as recently documented by Richards ["Sound Levels in the Human Uterus", Douglas S. Richards, M.D., Barbara Frentzen, M.S.N., Kenneth J. Gerhardt, Ph.D., Mary McCann, M.A., and Robert M. Abrams, Ph.D., Obstetrics and Gynecology, 1992; 80:186-190], and the presence of low frequency sound pressures can be considered as more harmful to the developing ear than to the adult ear. However, significant attenuation above frequencies of 1000 Hz occurs in the fluid-filled inner ear structures of the fetus ["Cochlear Microphonics Recorded from Fetal and Newborn Sheep", Kenneth J. Gerhardt, Ph.D., Randal Otto, M.D., Robert M. Abrams, Ph.D., Joy J. Colle, M.A., David J. Burchfield, M.D., and Aemil J. M. Peters, American Journal of Otolaryngology, July-August, 1992; 13(4):226-233].
Existing sound level meters often incorporate a weighting network to calculate pressures that may be harmful to the human adult ear including higher frequencies. Regulations use dB(A) weighting networks that reduce the contribution of low frequencies for calculating sound pressure levels. Thus, existing sound level meters do not reflect the possible pressure in the vicinity of a human fetal head.